Core, peel, and slice the apples in ½-inch pieces.
Place the apples into the skillet. Sprinkle the granulated sugar on top and the apple pie spice. Pour the apple juice on the apples and mix well. Cube the unsalted butter and place on top of the apples.
Cook on medium-high heat with lid on for 10 minutes. The apples will begin to soften. Reduce the heat to low and simmer for an additional 5-10 minutes.
Once the apples are soft (but not mushy), mix together the slurry of cornstarch and water. Slowly pour the cornstarch mixture into the apples, mixing continuously so the cornstarch does not clump.
Cook for an additional minute until thick glaze has formed. Remove from the heat and enjoy immediately.
Cast Iron Skillet - If you own a cast iron skillet use that instead of a non-stick pan. Something about the skillet that gives these apples a better flavor.
Corn Starch - I have found that using a corn starch slurry over an all-purpose flour slurry yielded a thicker more pure syrup.
Butter - If you aren 't dairy free you can add a touch of butter while the sauce begins to thicken.
Dairy Free - You can omit the butter if you are lactose intolerant or simply trying to avoid dairy.
Juice - I've tried both apple juice and apple cider. They both yield the same taste. So no differences there.
Spices - I also tested using cinnamon and nutmeg verse apple pie spice, and at the end of the day I liked the apple pie spice mixture (and simplicity of measuring once) .